Viscosity monitoring with a piezoelectric quartz crystal and its application to determination of endotoxin by gelation of limulus amebocyte lysate

A piezo-electric quartz crystal is used to monitor viscosity changes in a liquid. A resistance, included in the electrical equivalent circuit of the crystal, and the resonance frequency change of the crystal, measured by an impedance analyzer, are used for the viscosity measurement. Endotoxin concentrations are determined with this system by the gelation of Limulus amebocyte lysate. The gelation time is computed by using an approximation to a polynomial equation from the resistance or the resonance frequency change. The gelation time measured was in good agreement with that obtained conventionally. The detection limit is 1 pg ml^?1. The maximum rate of change of the resistance was confirmed as a good index of endotoxin concentration in order to shorten the measurement time to ? 40 min. The changes in the resistance or resonance frequency were also considered as indices of endotoxin concentration.